1. Field of the Invention
This invention generally relates to sewer pipe systems and more particularly to liquid-filled seals especially adapted for joining adjacent pipes in such sewer systems.
2. Description of Related Art
A conventional sewer system includes a network of pipes and manholes. Individual pipes in such systems typically have a spigot end and a bell or socket end. The pipes lay end-to-end with a spigot end of one pipe nested in the bell or socket end of an adjacent pipe. These joints are sealed to prevent leakage through the joint in both directions.
More specifically, such seals must prevent both the leakage of sewage from within the pipes to the surrounding ground and the leakage of ground water into the sewer system. The later sealing requirement is particularly important when sewage treatment facilities process the sewage. Sewage treatment systems must operate below a maximum design flow rate if the sewage processing is to be effective. If ground water infiltrates the system through the pipe joints, the total flow of sewage and infiltrated ground water, particularly during rainstorms, can exceed this maximum design flow rate. When this occurs, the effluent from the treatment facility will not be within acceptable standards.
The prior art uses several approaches for forming the joints between adjacent pipe sections in sewer systems. Initially the joints were packed with grout or cement. However, this approach is unsatisfactory because pipes can move, even when buried, and crack the grout thereby breaking the seal. The following patents disclose seal structures for use between the spigot and socket ends of adjacent lengths of sewer pipe:
6,892 (1879) Oesten (Germany) PA1 93,494 (1962) Nielsen (Denmark) PA1 3,258,271 (1966) Hollingsworth PA1 3,339,931 (1967) Hundt PA1 4,159,829 (1979) Ditcher PA1 4,269,419 (1981) Brant PA1 4,508,355 (1985) Ditcher PA1 829,546(1906) Schou PA1 1,966,209 (1934) pfefferle PA1 3,007,600 (1961) Horner PA1 3,038,732 (1962) Scott PA1 3,147,016 (1964) Traufler PA1 4,300,775 (1981) Ringel
The Oesten patent discloses a seal comprising an annular, hollow, smooth walled, flexible liquid-filled conduit. personnel must bring equipment to the installation site for pumping water into the conduit.
The Nielsen patent discloses a hollow sealing member that is evacuated, forced between overlapping portions of the spigot and socket ends of a pipe and then reinflated to atmospheric pressure. This compresses the seal between the overlapping portions of the spigot and socket ends.
The Hollingsworth patent discloses a seal in the form of an annular hollow ring of elastic inflatable material with an oval cross section and parallel ribs or ridges. After the seal is located about the spigot end of a pipe and the pipe is installed the bell end of an adjacent pipe, equipment at the installation site forces a mass of filling material in liquid form, into the ring under pressure. This mass solidifies under normal conditions of use.
The Hundt patent discloses an annular, oval, hollow gasket with a wick of a tube or flat sheet of fibrous felt in the cavity. Equipment at the installation site injects a resin into the cavity under pressure. The resin forms a hardened mass around the wick.
The Oesten, Hundt and Hollingsworth patents all require the presence of equipment at the site solely for installing a seal. Although the Nielsen patent discloses a seal formed by admitting ambient air into a seal, the pressure exerted by ground water in sewer pipe applications can break such a seal.
The following patents disclose annular, hollow seals used between a pipe and a manhole wall:
Both Ditcher patents disclose annular gaskets that surround the surface of a pipe as it penetrates a manhole wall. portions of each seal key into the manhole wall, thus requiring either complicated on-site installation or the construction of preformed manholes at the factory. One of the Ditcher patents discloses an annular, hollow, pear-shaped head with a single continuous passage; the other Ditcher patent discloses multiple passages. These passages are air-filled and provide a pneumatic cushion for the pipe.
Brant discloses a seal for insertion between two cylindrical objects that has rectangular ridges about the exterior. A liquid pressurizes this seal.
The following patents disclose liquid-filled seals generally used for other applications:
Schou discloses an annular packing member with a square cross-sectioned ring filled with liquid. The outer sealing surfaces are smooth.
Pfefferle discloses a smooth surfaced, liquid-filled gasket. This gasket seals pipes containing fluid at a high pressure.
Horner shows a liquid-filled seal between an end plate and a chamber. The chamber contains a fluid under pressure.
Scott discloses an inflatable annular bushing that surrounds and positions a central pipe in an outer casing.
Traufler discloses a metal-clad gasket for insertion between flanges on adjacent lengths of pipe. The gasket has corrugations to improve gasket resiliency and resistance and seals against the escape of fluid at high pressure from the pipe.
Ringel discloses a gasket for insertion between a stationary member and a concentric rotating member. The gasket lies in a groove in the stationary member to be fully supported thereby and contains a liquid. This seal is designed for containing lubrication or other materials.
The foregoing patents that are directed to interconnecting adjacent sections of pipe are all characterized by requiring special installation equipment that must be brought to the site. The disclosed patents for sealing between pipes and manhole walls require similar equipment. The various liquid-filled seals are directed to applications with sealing requirements that differ from those in sewer pipe applications.